add Android.mk files to enable building in tree

  to use the library in your app, edit the apps Android.mk

   1. built from source

        add the following line
        LOCAL_STATIC_JAVA_LIBRARIES := ListViewAnimations

   2. use prebuilt jar

        add the following line
        LOCAL_STATIC_JAVA_LIBRARIES := listviewanimations_prebuilt

Signed-off-by: Arnav Gupta <championswimmer@aokp.co>